Asthma is the most common pediatric chronic condition, affecting 9% of children and adolescents in the United States. Children with asthma are at increased risk for influenza-related morbidity and hospitalizations. Thus, for more than 50 years, annual influenza vaccination has been recommended for children with asthma. There are currently two influenza vaccine formulations, the inactivated influenza vaccine (IIV), administered intramuscularly, and the live attenuated influenza vaccine (LAIV), administered intranasally. Starting in 2014, the Advisory Committee on Immunization Practices (ACIP) recommended LAIV preferentially over IIV in healthy children due to its increased efficacy in preventing culture confirmed influenza and ease of administration. However, due to persistent concerns regarding vaccine safety, asthma at any age and recurrent wheezing in children younger than 5 years are both precautions for administering LAIV. HealthPartners Medical Group (HPMG) and Park Nicollet Health Services (PNHS) are two large medical groups serving demographically similar populations but operating under independent clinical leadership within HealthPartners, a Minnesota-based nonprofit integrated health care system. Beginning with the 2010-11 influenza season, HPMG implemented a policy recommending LAIV preferentially (rather than IIV) for all pediatric patients, including those with asthma or a history of wheezing. In contrast, the standard of care PNHS for the 2010-11 through 2104-15 influenza seasons has been to follow ACIP guidelines and recommend IIV (and not LAIV) for patients with asthma or children 2 to 4 years of age with a history of wheezing. We propose to use this unique natural experiment to evaluate the safety of an LAIV policy compared with an IIV policy using a ratio-of-ratios approach among nearly 40,000 vaccine doses administered to more than 23,000 pediatric patients with asthma or a history of recurrent wheezing. The proposed study will address crucial questions about risks of wheezing in asthmatic children after receiving LAIV. Findings from this study would have immediate policy implications, and ultimately may improve the health of children and adolescents with asthma. Furthermore, the methodology developed in this R21 proposal for classifying asthma severity and control with automated data is scalable and will be used in a future large-scale observational study or pragmatic trial LAIV safety and effectiveness.